Electrical bushings



Sept. 23, 1958 J. H. FRAKES 2,853,538

ELECTRICAL BUSHINGS Filed Sept. 28, 1953 4 Sheets-$heet 2 Sept. 23, 1958J. H. FRAKES ELECTRICAL BUSHINGS 4 Sheets-Sheet 3 Filed Sept. 28. 1953Sept. 23, 1958 .1. H. FRAKES ELECTRICAL BUSHINGS 4 Sheets-Sheet 4 FiledSept. 28, 1953 United States Patent ELECTRICAL BUSHINGS James H. Frakes,Pittsburgh, Pa., assignor to Westinghouse Electric- Corporation, EastPittsburgh, Pa., a corporation of Pennsylvania Application September 28,1953, Serial No. 382,721

8 Claims. (Cl. 174-12) This invention relates to terminal bushings ingeneral, and more particularly to terminal bushings of the highvoltagetype in which one or more Weatherproof casings of an insulatingmaterial, such as porcelain, are maintained in compression, whereas aninteriorly disposed stud or conducting tube is maintained in tension.

The general objectof my invention is to provide an improved terminalbushing which will be adaptable for all" conditions of service, whichmay include its use in circuit breakers where high-fault currents areinterrupted.

A more specific object of my invention is to provide an improved dashpotassembly associated with .a terminal bushing of the type employingspring pressure to maintain the Weatherproof casing of the terminalbushing under compression, to prevent thereby excessive mechanical andelectrical shock to the bushing.

It has been observed during the interruption of highfa-ult currents incircuit breakers of the liquid-break type involving a pair ofhigh-voltage terminal bushings, that vibration and mechanical shockoccurring during such high-fault current interruption tends to compressthe gaskets and the porcelain casings during a portion of such operationand, on the other hand, to permit excessive relaxing of the gaskets sothat on certain occasions oil may leak out of the high-terminal bushingat the gaskets during such high-fault current interruption.

It is a further object of my invention to associate an improved andhighly effective dashpot arrangement with the spring assembly, generallydisposed in the cap of a high-voltage terminal bushing, to preventsudden movement', or to damp large scale differential movement betweenthe interiorly disposed conductor stud and the surrounding Weatherproofcasing elements.

Still a further object is to provide a dashpot assembly associated witha terminal bushing of the type utilizing a compression spring assemblyin which sudden difierential movement between the interiorly disposedterminal stud and the surrounding weatherproof casing elements isdampened to prevent mechanical or electrical shock to the bushing.

Further objects and advantages will readily become apparent upon readingthe following specification, taken in conjunction with the drawings, inwhich:

Figure 1 shows a side elevational view, partially in vertical section,of a high-voltage terminal bushing, in this instance one of thecondenser-wound type, with a portion of the cap assembly broken away toindicate the spring assembly;

Fig. 2 is an enlarged fragmentary vertical sectional view taken throughthe upper cap assembly of the terminal bushing illustrated in Fig. 1;

Fig. 3 is a plan sectional view taken through the cap assembly of Fig.2, substantially along the line IIIIII thereof;

Fig. 4 is a broken plan sectional view, taken substantially along theline IVIV of Fig. 2;

Fig. 5 is an enlarged vertical sectional view through the improveddashpot assembly utilized in my invention,

Patented Sept. 23, 1958 ICC 2 indicating its relative position withrespect to the spring cap and spring base plate castings;

Fig. 6 is a plan view taken along the line VI-VI of Fig. 5;

Fig. 7 is a vertical sectional view taken through the top spring cap ofthe spring assembly;

Fig. 8 is a vertical sectional view taken through the lower spring baseof the spring assembly; and,

Fig.- 9 illustrates a modification of my invention in which adouble-acting dashpot dampens both excessive sudden elongation of thespring assembly and also excessive sudden compression of the springassembly.

Referring to the drawings, and more particularly to Fig. 1 thereof, thereference numeral 1 generally designates a terminal bushing of the typeemployed in the cover of a circuit breaker of the liquid-break type, ora circuit breaker of any type disposed interiorly within a suitable tankstructure. Also, such a terminal bushing 1 may be employed in connectionwith a transformer, by which the leads to the transformer may be broughtexteriorly of an enclosing housing through two such terminal bushings-1.

It will be observed that the high-voltage terminal bushing 1 includes alower porcelain support 2, which is screwed onto a lower threadedportion of a copper condenser tube, or terminal stud 3, the latterextending axially interiorly throughout the length of the terminalbushing 1. The lower porcelain support 2 abuts against a lowerweatherproof casing, in this instance formed of porcelain, designated bythe reference numeral 4, with a gasket, not shown, interposedtherebetween. At the upper end of the lower porcelain 4 is anintermediately disposed flange assembly 6, which may be employed tomount the terminal bushing 1 upon a suitable tank, or housing, forelectrical equipment, with which one or more of the terminal bushings 1may be utilized.

Disposed upwardly from the flange assembly 6, which is generally atground potential, is an upper weatherproof casing 7, in this instanceformed of porcelain. Disposed at the top of the terminal bushing 1 is acap assembly, generally designated by the reference numeral 9, andincluding a spring assembly 10 comprising, in this instance, severalcompression springs acting to maintain the porcelains 4 and 7 undercompression, with the longitudinally extending copper condenser tube 3under tension.

In this particular instance, the terminal stud 3 is of tubularconfiguration and carries the electrical current through the terminalbushing 1 itself, or, in certain instances, a terminal lead from theelectrical apparatus may be fished through the hollow condenser tube 3,and be attached at the upper end thereof. As is customary in the art,because of the high voltage of the condenser tube 3, preferablycapacitance shielding is employed to properly grade the voltage betweenthe terminal stud 3 and the grounded flange assembly 6. This may includewrapping the condenser tube 3 with oil-impregnated paper and having atcertain intervals metallic foil to provide the series plates of such acondenser. The upper and lower porcelains 4 and '7 protect theinteriorly disposed terminal stud 3, with its condenser Wrapping, fromthe weather, and, as mentioned, the fiange assembly 6 at groundpotential is employed to suitably mount the terminal bushing 1 upon aproper housing. Oil fills the casings 4 and '7 about the condenserwrapping for high dielectric strength.

Referring to Fig. 2, which more clearly illustrates the internalconstruction of the upper end of the terminal bushing 1, and morespecifically the spring assembly 10 therefor, it will be observed thatthe condenser tube 3 is shown partly in section and has the upper end 11threaded, as at 12, to receive an interiorly threaded sleeve 13, thelatter being a portion of a spun cap assembly 15.

The spun cap assembly includes a copper diaphragm 16, which may flex toaccommodate longitudinal differential movement between the condensertube 3, which is under tension, and the surrounding porcelain casings 4,7 which are under compression. The upper end of the copper diaphragm 16is brazed to a thimble 17, the latter in turn being brazed to the sleeve13. The lower end of the copper diaphragm 16 is brazed into a slot 18formed at the upper end of a cap shell 19.

A dial 20 indicates to an observer the level of oil, which fills theinterior chamber 21 within the casings 4, 7 and the cylindrical flangeassembly 6. Associated with the dial 20 is a gauge mechanism float 22which floats upon the surface of the oil, and causes a proper indicationof the oil level on the dial 20.

The spring assembly 10 includes a top spring cap 24, the configurationof which is more clearly shown in Fig. 7 of the drawings. It will beobserved that at the lower end of the top spring cap 24 are a pluralityof apertured bosses 25, which serve as upper seats for a plurality ofcompression springs 26.

The lower ends of the compression springs 26 seat upon a spring base 27,the configuration of which is more fully apparent from an inspection ofFig. 8 of the drawings. The spring base 27 has a plurality of aperturedand tapped bosses 28, which accommodate a plurality of bolts 29, thedisposition of which is more fully apparent from Fig. 2 of the drawings.Thus, the bolts 29 slide through the apertures 30 in the bosses of thespring cap 24, pass interiorly through and guide the compression springs26 and are threadedly received interiorly within the tapped apertures 31provided in the spring base 27.

As will be obvious to those skilled in the art, the bolts 29 areemployed to precompress the compression springs 26 prior to assemblyupon the condenser tube 3. In other words, the bolts are threaded intothe tapped apertures 31 until a proper separation distance existsbetween the gauge points 32, 33, more clearly shown in Fig. 2. The lowergauge point 33 consists of a pin 34 driven by a press fit within thespring base 27, whereas the upper gauge point 32 may comprise merely adownwardly extending boss 35 integrally cast with the top spring cap 24.The separation distance between the gauge points 32, 33 indicates theamount of precompression of the several springs 26, which, together withthe spring plates 24, 27, and an interiorly disposed insulating sleeve36, collectively constitute a sub-assembly which may he slid upon thecondenser tube 3 during the assembly of the terminal bushing 1.Following the threading of the condenser tube 3 interiorly through thespring assembly 10, a spacing sleeve 37 is mounted about the condenserstud 3, after which the spun cap assembly 15 encircles the terminal stud3 and is threadedly secured thereto.

Following such an operation, the lifting lug nut 38 is threadedlysecured over the sleeve 13 and brazed thereto to provide an oil-tightjoint. Then follows a gasket 39 and an adaptor cap 40, which is securedin place by a plurality of machine bolts 41 screwed into tappedapertures 42 provided in the lifting lug nut 38.

With porcelain casing 4 clamped between lower porcelain support 2 andgrounded flange assembly 6, pressure is applied between flange assembly6 and thimble 17 to compress springs 26 to the required pressure, asdetermined by the gap distance between gauge points 32 and 33. Sleeve 13is then screwed down against thimble 17 to hold springs 26 incompression. At this stage, the bolts 29 are loose to permit the springpressure exerted by the several compression springs 26 to place theporcelain casings 4 and 7 under compression and the conductor stud 3under tension.

-The foregoing structure has been found to provide a desireddiiferential movement between the terminal stud 3 and the porcelains 4and 7 during operation of the w of the, drawings.

terminal bushing 1, with expansion of the oil within the chamber 21accommodated, all being caused by temperature changes. Preferablynitrogen gas is disposed above the oil level to prevent oxidation of theoil.

When the terminal bushing 1 is used in circuit breaker installations, orin other installations, where excessive mechanical or electrical shocksare encountered, sudden compression of the springs 26 may permit leakageof oil to take place outwardly from the chamber 21 past the gaskets, oneof which is shown near the lower end of Fig. 2, and is collectivelydesignated by the reference numeral 43. It comprises a pair ofconcentrically disposed gaskets, one of which 43a may be resilient andprovide a fluid-type joint, whereas the outer one 431;

' provides a stop to limit excessive compression of the internal gasket43a. Should the compression springs 26 be compressed suddenly, excessiveoil may leak past the gasket 43, which action of course is highlyundesirable, as it will necessitate refilling the oil within thecondenser bushing 1.

To prevent such sudden excessive vibration and mechanical shock takingplace, I associate a dashpot means, generally designated by thereference character 45, with the spring assembly 10, as more clearlyshown in Fig. 5 The dashpot assembly 45 comprises a loweroperating-cylinder plate 46 having a plurality of operating cylinders 47provided therein, which vent through small leak apertures 48 to theregion 21 within the casings 4 and 7. Operating within the severalcylinders 47 are a plurality of pistons 49 biased upwardly to a limitingposition against the top spring cap 24 by a plurality of relativelylight compression springs 50. The compression springs 50 constantlymaintain the tops 51 of the pistons 49 against the top spring plate 24.For clarity of illustration, the compression springs 26 have beenomitted from Fig. 5.

Fig. 6 illustrates a top plan view taken on the dashpot means 45,showing the tops 51 of the pistons 49, and illustrating how the casting46 may have a quarter section removed therefrom, as at 52, to permit itsencirclement of the condenser stud 3.

It will be obvious that should a sudden compression ofthe compressionsprings 26 attempt to take place, the oil disposed back of the pistons49 will prevent sudden compression of the springs 26 taking place. Thiswill prevent leaking at the several gaskets 43.

Fig. 9 shows a modification of the invention wherein the dashpot means45a includes a double-acting dashpot assembly, including plungers 53integrally formed with the top spring cap 24a. A plurality of operatingcylinders, or cavities 54, are integrally formed with the lower springplate 27a, and again bleeder openings 48 are provided to restrict oilflow out of the piston chambers 55. It will be observed that themodified dashpot is doubleacting so that it will prevent suddencompression of the springs 26, and sudden elongation thereof, sincesuction will occur during elongation of the springs 26, and compressionof the oil within the piston chambers 55 will occur upon suddencompression of the springs 26.

From the foregoing description of my invention, it will be apparent thatI have provided an improved dashpot means associated with the springassembly to maintain continuous pressure on the gasket joints ofhighvoltage bushings regardless of expansion or contraction of the partswith temperature changes. Experimental tests have shown that on highinterrupting kva. breakers the bushings, which are subject to electricaland mechanical forces during heavy short-circuit current interruptionwill not permit sudden compression of the springs 26 taking place due tothe action of the dashpot means 45. Therefore, sudden movement tendingto release pressure on the gasket seals to cause opening, or to puttremendous pressure on the gasket or bushing parts is avoided. I haveutilized an oil dashpot located between the spring compression pointsand below the oil level in the bushing.

This dashpot restrains any sudden movement of the springs by forces asencountered during breaker heavycurrent interruption, but has sufiicientleakage of oil to permit slow spring movement with expansion andcontraction due to temperature cycles.

The several pistons fit closely within their cylinders, and the lightsprings 50 hold the pistons 49 in proper position. The small bleederopenings 48 permit oil to flow slowly in and out of the operatingcylinder when necessary. When the piston moves up and down slowly in thecylinder, oil runs in or out of the holes 46 in the cylinders to permitmovement. When a sudden pressure on the bushings tries to move thepiston down in the cylinder, the oil does not have time to escapethrough the small hole 48, and the oil blocks the sudden movement of thepiston 49. This oil dashpot is for keeping the springs 26 fromcompressing suddenly, and the plungers 53 in the double-acting dashpotarrangement of Fig. 9 prevent the sudden compression or elongation ofthe springs 26 in Fig. 9.

Incorporating the dashpot assembly 45 within the terminal bushing 1.results in the terminal bushing 1 being utilized in connection withhigh-voltage fault current interruption without leakage of terminalbushing oil taking place through one or more of the gasket seals 43.Moreover, excessive stress upon the porcelains 4 and 7 has beeneliminated and the terminal bushing 1, as a whole, is adapted forapplications involving mechanical and electrical shock.

Although I have shown and described specific structures, it is to beclearly understood that the same were merely for the purpose ofillustration, and that changes and modifications may readily be madetherein by those skilled in the art, without departing from the spiritand scope of the invention.

I claim as my invention:

1. A terminal bushing including a longitudinally extending tensionmember, one or more casing elements, spring means for placing the casingelements under compression and the tension member under tension, anddashpot means including a piston for preventing sudden difierentialmovement between the casing elements and the tension member.

2. The combination in a terminal bushing of one or more casing elementsand an interiorly disposed conducting tension member, spring means forexerting tensile stress on the conducting tension member and compressivestress on the casing elements, and dashpot means including a piston forpreventing sudden relative movement between the two.

3. A terminal bushing including a longitudinally extending tensionmember, one or more casing elements, spring means including a pluralityof compression springs tor exerting tensile stress on the tension memberand mum pressive stress on the casing elements, and a dashpot includinga piston for preventing sudden compression of the compression springs. i

4. The combination in a terminal bushing of one or more casing elementsand an interiorly disposed conducting tension member, spring meansincluding a plurality of compression springs for exerting tensile stresson the tension member and compressive stress on the casing elements, anda dashpot including a piston for limiting sudden difierential movementbetween the tension member and the casing elements.

5. The combination in a terminal bushing of the type wherein biasingmeans exerts tensile stress on a longitudinally extending tensile memberand compressive stress on one or more casing elements, characterized bya dashpot including a piston to prevent sudden movement of the biasingmeans.

6. A terminal bushing including a longitudinally extending tensionmember, one or more casing elements, spring means including a battery ofcircularly disposed compression springs for exerting tension on thetension member, a pair of spring plates, and a dashpot including aplurality of concentrically arranged piston elements for preventingsudden difierential movement between the tension member and the one ormore casing elements.

7. A terminal bushing including a longitudinally extending tensionmember, one or more casing elements, spring means for placing the casingelements under compression and the tension member under tension, and adouble-acting dashpot including a piston for preventing suddendifferential movement between the casing elements and the tensionmember.

8. The combination in a terminal bushing of one or more casing elementsand an interiorly dispose-d conducting tension member, spring means forexerting tensile stress on the conducting tension member and compressivestress on the casing elements, and a double-acting liquid dashpot forpreventing sudden relative movement between the two.

References Cited in the file of this patent UNITED STATES PATENTS1,821,787 Black Sept. 1, 1931 1,869,475 Hale Aug. 2, 1932 2,285,594Lingal June 9, 1942 2,292,031 Arnold Aug. 4, 1942 2,569,503 ThelanderOct. 2, 1951 FOREIGN PATENTS 820,020 France Oct. 30, 1937

